The present invention relates to generally a traverse motion used in an apparatus for winding continuous elongate elements around spools and more particularly a traverse motion adapted to produce large-diameter packages of strands each consisting of a large number of glass filaments having a large diameter.
In general, conventional bushings used for the production of glass fibers are provided with 400 to 800 orifices and glass filaments drawn through such bushings are 10 to 13 microns in diameter. In order to produce large-diameter roving packages from such glass filaments, two production steps are needed. In the first step, 400 to 800 glass filaments drawn through a single bushing are gathered into a strand which in turn is formed into a tapered cake. In the second step, strands are rewound from 15 to 30 cakes and gathered into a single roving which in turn is wound around a spool.
However, the spinning technique has been recently so developed that 2000 to 4000 glass filaments of 15 to more than 20 microns in diameter can be simultaneously drawn through a single bushing and can be gathered into a single strand which in turn is wound around a spool to directly produce a package of a desired diameter. That is, the finished package can be produced by a single step. As a result, high productivity can be attained, but if the prior art winding apparatus is used without any modification, packages of high quality cannot be produced. The requirements for high-quality packages are (1) that each package must have ends which are substantially at right angles to the axis of the package and which are parallel with each other; (2) that the cylindrical surface must be smooth; that is, it must be free from any ridge and valley so that the package must be ideally in the form of a true cylinder with square ends; (3) that the entire length of strand must be uniform in diameter and free from fuzz; (4) that the hardness of the package must be uniform from the cylindrical surface to the core; and (5) that the strand can maintain its stable form even after it has been unwound from the package and impregnated with resins in the succeeding stage.
In the production of such high-quality packages, there exists a problem that due to the delay in response of the motion of the strand to that of the strand guide of a traverse motion, the strand dwells at each of the ends of its reciprocal motion so that the diameter of a finished package becomes greater at the ends than in the intermediate portion thereof. In addition, the higher the traversing speed, the more pronounced the difference in diameter between the ends and the intermediate portion of the finished package. In order to overcome this problem, there has been used a pressure roller which is constantly pressed against the cylindrical surface of a package being formed, thereby making the surface flat. Under such a condition that the non-uniform form of the package is more pronounced, however, the pressure applied to the package being formed is so high that the finished package is deformed. As a result, the strand in the vicinity of the ends of the package is flattened and hardened and tends to slip off from the ends, thereby to destroy the end shape.
In order to solve this problem, the inventors proposed an improved traverse motion whose scroll cam has a specially designed cam groove profile in U.S. Pat. No. 4,383,653. In that traverse motion, the lead angle of an endless helical cam groove is increased at the ends of the scroll cam so that the strand guide can be accelerated at each end of its reciprocating motion. Therefore, the dwell of the strand at the ends of the reciprocating motion of the strand guide can be eliminated by the acceleration of the motion of the guide so that packages with square ends can be produced without the use of a pressure roller. In addition, if a pressure roller is used, an optimum pressure can be applied to the whole cylindrical surface of a package being formed so that the high-quality finished package can be obtained.
The above-described traverse motion, however, has a problem that the cam follower finds it difficult to faithfully follow the cam groove in the vicinity of the turning points of motion at each end of the cam where the lead angle is increased as described above. In general, a ship-shaped cam follower has been used in conjunction with a scroll cam so that it can pass smoothly the intersections between the right- and left-hand cam grooves. This ship-shaped cam follower cannot faithfully follow the cam groove portions where the lead angle is increased as described above.